The majority of modern cable telecommunications systems used today are built with a Hybrid Fiber Coax (HFC) network topology. This topology uses fiber optic cable to transmit optical signals to and from a fiber optic node located near a cable subscriber, such as a residential home, subscribing to cable telecommunication services. The fiber optic node receives and converts the optical signals into Radio Frequency (RF) signals. These RF signals are then transmitted from the fiber optic node to the subscriber's home over a coaxial cable.
FIG. 1 illustrates a conventional HFC network 100. The HFC network 100 includes a head-end 102. The head-end 102 is a facility for receiving, processing, and distributing media signals, including video, audio, and data signals, over the HFC network 100. The head-end 102 is typically maintained or managed by a media service provider, such as a cable television (CATV) provider or an Internet service provider (ISP). The head-end 102 may include any reasonably suitable electrical equipment for receiving, storing, and re-transmitting media signals, such as media servers, satellite receivers, modulators/demodulators, edge decoders, etc. The head-end 102 may transmit the media signals downstream to subscribers 110, over a fiber optic link 104 to one or more fiber optic nodes 106, each supporting any number of subscribers 110, depicted here as residential homes. While, the subscribers 110 may include a plurality of individual residential homes or premises, a person having ordinary skill in the art will appreciate that the subscribers 110 may, of course, include multi-unit dwellings and commercial premises that subscribe to media content services. Each fiber optic node 106 receives and converts the optical signals sent from the head-end 102 into RF signals, which are then delivered to the subscribers 110, via coaxial cables 108.
Conventional HFC networks, such as the network 100, typically employ various methods or sending desired signals over a coaxial cable, such as the coaxial cables 108. One common method is data over cable service interface specification (DOCSIS), which is an international standard that defines the communications and operation support interface requirement for a data-over-cable system. DOCSIS permits the addition of high speed data transfer to an existing cable TV system and is employed by the majority of multiple-service operators (MSOs) to provide Internet, real-time interactive gaming, video conferencing, video on-demand services, etc. over existing HFC networks. DOCSIS includes two primary components: at least one piece of subscriber equipment, such as a cable modem and/or a multimedia terminal adapter (MTA), located at a subscriber's premises and a cable modem termination system (CMTS) located at the head-end 102. In the upstream data path, the subscriber equipment generates a data signal, which is transmitted for interpretation by the CMTS, as described in greater detail below.
In recent years, new housing developments have been built with fiber optic links (e.g., fiber optic cables) extending near, or directly to, the subscribers 110 and, in some cases, no longer provide coaxial cable links to the subscribers 110. These fiber-to-the-premises (FTTP) architectures operate essentially by moving the fiber optic node 106, depicted in FIG. 1, to each of the subscribers 110. Therefore, optical signals are delivered directly to each subscriber's premises. While the use of coaxial cable 108 is reduced, these modern architectures may still be considered HFC networks because they utilize coaxial cable within the subscriber's premises. However, MSOs do not currently have a cost effective technology to deliver their RF signals over fiber in FTTP architectures and are, therefore, at a competitive disadvantage in such circumstances. Furthermore, because of the very large investment MSOs have made in DOCSIS equipment for existing HFC networks, it is desirable for the MSOs to have a FTTP solution that can leverage such equipment.
One apparent solution is to place a fiber optic node at each subscriber 110. In such a solution, optical signals are delivered directly to each subscriber 110, such as a residential home, which are then converted by the fiber optic node 106 into RF signals for transmission through one or more coaxial cables to one or more pieces of subscriber equipment therein. This is conceptually simple for the downstream signals (signals sent down or downloaded from the head-end 102 to the subscribers 110) and is, in fact, being utilized by known passive optical network (PON) architectures with video overlays. Such a fiber optic node at the subscriber's premises is commonly called an optical network terminal (ONT).
With the increasing use of Internet and interactive television services, such as video on-demand, the previously seldom-used upstream signals have garnered increased attention. As understood in the art, upstream or return path signals, refer to data generated by the subscriber's equipment for transmission back to the head-end 102 or media service provider. Examples of common subscriber equipment, which generate upstream signals include, but are not limited to, set top boxes (STBs) used for cable television services, cable modems used for high-speed internet and e-mail services, and MTAs for voice over Internet protocol (VoIP) services. Thus, upstream signals may include data and control information from such devices. For example, a subscriber 110 may select a particular on-demand movie or television program. This selection is sent back to the head-end 102 so that the selected movie or television program may be provided to the subscriber 110. Typically, upstream data signals are sent from the subscribers 110 to the head-end 102 as digital signals modulated on analog RF carrier signals, which are produced by the subscriber equipments.